As the semiconductor industry migrates to 90 nanometer and smaller technologies, the minimum distance between adjacent interconnect lines grows smaller. Inter-level dielectric materials (ILD) such as silicon oxide are being replaced by low-k dielectric materials, to reduce the capacitance between nearby interconnect lines. At the 32 and 45 nanometer nodes, the capacitance problem is even more acute. Typical methods to reduce capacitance between interconnect lines use an ILD (Inter-Layer-Dielectric) or IMD (Inter-Metal-Dielectric) material with a lower k value, such as FSG, carbon-doped silicon oxide(e.g., BLACK DIAMOND) and extreme low-k (ELK) dielectrics having a k value less than 2.5 to reduce interconnect capacitance.
Dielectric materials with reduced k have a lower mechanical strength. There are many reliability issues when using ELK dielectrics, in particular packaging problems. ELK film strength is about 50% weaker than low-K. When ELK and ultra low-k (ULK) materials are used, the thermal mismatch between the die and the package substrate can cause cracking and/or delamination of the ILD material. Use of ELK also has a high cost. Integration of ELK requires a very complicated process flow (e.g. pore sealing, UV/e-beam cure, and the like), which increases cost and cycle time. ELK has a low thermal conductivity (<0.2 W/m−C), which impedes thermal dissipation and causes electromigration and other thermal related reliability problems.
U.S. Patent Application Publication No. US 2005/0074961 describes a method for the production of air gaps in a semiconductor device. Air is used for its dielectric and insulation properties. The formation of air gaps is accomplished, in part, by chemically and/or mechanically changing the properties of a first dielectric layer locally, such that at least part of the first dielectric layer is converted locally and becomes etchable by a first etching substance. The local conversion of the dielectric material may be achieved during anisotropic etching of the material in oxygen containing or fluorine containing plasma or ex-situ by performing an oxidizing step (e.g., a UV/ozone treatment or supercritical carbon dioxide with addition of an oxidizer). Formation of air gaps is achieved after creation of conductive lines and, alternatively, a barrier layer by a first etching substance. The air gaps are formed in a dual damascene structure, near the vias and/or the trenches of the damascene structure.
Improved methods of reducing capacitance between interconnect lines are desired.